Multiplexed computer system

ABSTRACT

A multiplexed computer system allows memory accessing by a processor, a peripheral equipment or a like apparatus even during execution of memory copying to improve the processing performance during on-line maintenance. To this end, the multiplexed computer system includes a plurality of processing units which effect a same operation in synchronism with each other. Each of the processing units includes a copy processor register for designating a processor to read out contents of a memory unit, copying means for transferring copies of the stored contents of the memory unit and data to be written into the memory unit in the same order as that of accesses to the memory unit to a memory unit of the other processing unit, a copy mode flag indicating that memory copying processing for making the stored contents of the memory unit of the self system and stored contents of the memory unit of the other processing unit coincide with each other is proceeding, and a copy task flag indicating that the processor is reading out, during memory copying processing, the stored contents of the memory unit.

FIELD OF THE INVENTION

[0001] This invention relates to a multiplexed computer system, and more particularly to a multiplexed computer system in which memory copying for putting memories of the multiplexed computer system into coincidence with each other is effected.

BACKGROUND OF THE INVENTION

[0002] A conventional multiplexed computer system wherein a plurality of processing units execute a same calculation in synchronism with each other requires means for putting stored contents of memories of all of the processing units into coincidence with each other in order to allow the processing units to perform a same operation in synchronism with each other, that is, to perform a multiplexed operation again after one of the processing units is disabled because of a failure or a periodic inspection is performed for a particular one of the processing units.

[0003] As a method of putting stored contents of memories of all processing units which operate, for example, in a duplicated condition into coincidence with each other, the following two memory copying methods are adopted usually.

[0004] In particular, as the first memory copying method, in a computer system which operates in a duplicated condition, an operation of copying a fixed region of stored contents of a memory provided in one of processing units which is operating (hereinafter referred to as normal system processing unit) into another memory provided in another one of the processing units which is not operating (hereinafter referred to as abnormal system processing unit) using data transfer means of the normal system processing unit between a memory and a peripheral equipment, that is, so-called DMA engine, is repetitively executed after each fixed interval of time. Further, where a processor provided in the normal system processing unit is constructed so that it can access only the memory in the same processing unit, data to be written from the processor provided in the normal system processing unit into the memory of the same processing unit are transferred to the memory provided in the abnormal system processing unit. An example which discloses a technique regarding this is Japanese Patent Laid-Open Application No. Hei 3-182958.

[0005] As the second memory copying method, in a computer system which includes processing units which operate in a triplicated condition and global memories which operate in a duplicated condition and wherein each of the processing units includes a local memory and data transfer means between the local memory and the global memories, that is, so-called DMA engine, an operation of copying a fixed region of stored contents of one of the global memories which is operating (normal system) into the other global memory which is not operating (abnormal system) via the local memory provided in the processing unit using the DMA engine provided in the processing unit is repetitively executed after each fixed interval of time until all regions of the memory are copied. It is to be noted that, while the stored contents of the memory are being transferred, accessing to the global memories by a peripheral equipment, that is, DMA, is inhibited. A technique regarding this is disclosed in Doug Jewett, “Integrity S2: A Fault-Tolerant Unix Platform”, Twenty-First FTCS International symposium, Montreal, 1991.

[0006] A multiplexed computer system having an obstacle resisting function has a so-called on-line maintenance function of allowing repair or exchange a failed element while executing ordinary processing in order to allow a multiplexed operation to be performed again, and even while such on-line maintenance is performed, it is required to prevent deterioration of a processing performance. Accordingly, memory copying essentially required for on-line maintenance must be performed without making an obstacle to ordinary processing.

[0007] However, in memory copying in on-line maintenance, stored contents of the memory provided in the normal system processing unit which always vary by ordinary processing must be transferred to the memory provided in the abnormal system processing unit while maintaining the consistency, and the following problems which disturb this must be solved.

[0008] In particular, if the normal system processing unit reads out, immediately before certain regions of the memories provided in the normal system processing unit and the abnormal system processing unit are rewritten simultaneously by ordinary processing, the region of the memory thereof and transfers the thus read out data to the region of the memory of the abnormal system processing unit in order to perform memory copying, then after the regions of the memories of the normal system processing unit and the abnormal system processing unit are rewritten by ordinary processing, the data prior to such rewriting are copied into the region of the memory of the abnormal system processing unit. Consequently, the consistency between the memories of the normal system processing unit and the abnormal system processing unit is lost.

[0009] According to the first conventional method described above, memory coping is executed using the DMA engine provided in the normal system processing unit, and consequently, during execution of memory copying, DMA between the two system memories and a peripheral equipment by the DMA engine is not executed. Accordingly, during execution of memory copying, both of the memories are not rewritten by DMA, thereby solving the problem of the loss of the memory consistency described above.

[0010] Meanwhile, according to the second conventional system described above, memory copying is executed using a DMA engine provided in a processing unit, and consequently, during execution of memory copying, DMA between a local memory and the two system global memories by the DMA engine is not executed. Further, since DMA between a peripheral equipment and the two system global memories is inhibited during execution of memory copying, the two global memories are not rewritten by DMA during execution of memory copying, thereby solving the problem of the loss of the memory consistency described above.

[0011] However, those conventional methods have a problem in that, during execution of memory copying, DMA between a peripheral equipment and a memory and DMA between a local memory and a global memory cannot be executed. Further, they have another problem in that, since an operation of copying a fixed memory region by means of a DMA engine is executed repetitively after each fixed interval of time until all regions of the memory are copied, overheads by pre-processing for memory copying such as setting of a DMA engine or flushing of a cache memory are increased. It is to be noted that, since flushing of a cache memory is performed such that a region of the cache memory corresponding to a memory region to be copied is flushed before memory copying is executed and then, after copying of all of the memory regions is completed, the all regions of the cache memory are flushed again, cache flushing executed in memory copying is equal to the sum total of the memory capacity and the cache capacity. Those problems make causes of deterioration of the processing performance during on-line maintenance.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide a memory copying method for a multiplexed computer system composed of a plurality of processing units which allows memory accessing by a processor or a peripheral equipment even during execution of memory copying and minimizes overheads by pre-processing for memory copying.

[0013] In order to attain the object described above, there is provided a multiplexed computer system which includes a plurality of processing units which effect a same operation in synchronism with each other, and one or a plurality of peripheral equipments capable of accessing all of the processing units and wherein each of the processing units at least includes a processor or processors which effect operation processing, a cache and a memory unit which is accessible by the processor or processors and the peripheral equipment or equipments and the plurality of processing units are communicatable with each other, wherein each of the processing units includes copying means for transferring stored contents read out from the memory unit by the processor or processors and copies of data to be written into the memory unit by the processor or processors or the peripheral equipment or equipments in the same order as that of accesses to the memory unit, a copy processor register for designating one of the processor or processors which is to execute reading out of stored contents of the memory unit in order to effect memory copying, a copy mode flag for indicating that memory copying processing for making the stored contents of the memory unit of the self system and stored contents of the memory unit or units of the processing unit or units of the other system or systems coincide with each other is proceeding, and a copy task flag for indicating that the memory copying processing is proceeding and the processor is reading out the stored contents of the memory unit in order to transfer the stored contents of the memory unit of the self system to the memory unit or units of the processing unit or units of the other system or systems. Further, as another means for achieving the object described above, there is provided a multiplexed computer system which includes a plurality of processing units which effect a same operation in synchronism with each other, and one or a plurality of peripheral equipments capable of accessing all of the processing units and wherein each of the processing units at least includes a processor or processors which effect operation processing, a cache and a memory unit which is accessible by the processor or processors and the peripheral equipment or equipments and the plurality of processing units are communicatable with each other, wherein each of the processing units includes copying means for transferring stored contents read out from the memory unit by the processor or processors and copies of data to be written into the memory unit by the processor or processors or the peripheral equipment or equipments in the same order as that of accesses to the memory unit, a copy processor register for designating one of the processor or processors which is to execute reading out of stored contents of the memory unit in order to effect memory copying, verification means for comparing a latest address read out by the designated processor with an address of a write access to the memory unit from any of the peripheral equipment or equipments and, when a difference between the two values is smaller than a value determined in advance, instructing the copying means to transfer a copy of the data in the write access to the memory unit to the memory unit or units of the other processing unit or units, but, when the difference between the two values is larger than the value determined in advance, instructing the copying means not to transfer the copy of the write access data to the memory unit to the memory unit or units of the other processing unit or units, a copy mode flag for indicating that memory copying processing for making the stored contents of the memory unit of the self system and stored contents of the memory unit or units of the processing unit or units of the other system or systems coincide with each other is proceeding, and a copy task flag for indicating that the memory copying processing is proceeding and the processor is reading out the stored contents of the memory unit in order to transfer the stored contents of the memory unit of the self system to the memory unit or units of the processing unit or units of the other system or systems.

[0014] Further, as a further means for achieving the object described above, there is provided a multiplexed computer system which includes a plurality of processing units which effect a same operation in synchronism with each other, and one or a plurality of peripheral equipments capable of accessing all of the processing units and wherein each of the processing units at least includes a processor or processors which effect operation processing, a cache and a memory unit which is accessible by the processor or processors and the peripheral equipment or equipments and the plurality of processing units are communicatable with each other, wherein each of the processing units further includes memory read-out means for reading out stored contents of the memory unit successively from all regions of the memory unit beginning with a top address or a last address, copying means for transferring stored contents read out from the memory unit by the memory read-out means and copies of data to be written into the memory unit by the processor or processors or the peripheral equipment or equipments to the memory unit or units of the other processing unit or units in the same order as that of the accesses to the memory unit, a copy address register for indicating an address which makes an object of copying of the memory unit, and a copy mode flag for indicating that memory copying processing for making the stored contents of the memory unit of the self system with stored contents of the memory unit or units of the processing unit or units of the other system or systems coincide with each other is proceeding.

[0015] Further, as a further means for achieving the object described above, there is provided a multiplexed computer system which includes a plurality of processing units which effect a same operation in synchronism with each other, and one or a plurality of peripheral equipments capable of accessing all of the processing units and wherein each of the processing units at least includes a processor or processors which effect operation processing, a cache and a memory unit which is accessible by the processor or processors and the peripheral equipment or equipments and the plurality of processing units are communicatable with each other, wherein each of the processing units further includes memory read-out means for reading out stored contents of the memory unit successively from all regions of the memory unit beginning with a top address or a last address, copying means for transferring stored contents read out from the memory unit by the memory read-out means and copies of data to be written into the memory unit by the processor or processors or the peripheral equipment or equipments to the memory unit or units of the other processing unit or units in the same order as that of the accesses to the memory unit, verification means for comparing a latest address read out by the memory read-out means with an address of a write access to the memory unit from any of the peripheral equipment or equipments and, when a difference between the two values is smaller than a value determined in advance, instructing the copying means to transfer a copy of the data in the write access to the memory unit to the memory unit or units of the other processing unit or units, but, when the difference between the two values is larger than the value determined in advance, instructing the copying means not to transfer the copy of the write access data to the memory unit or units of the other processing unit or units, a copy address register for indicating an address which makes an object of copying of the memory unit, and a copy mode flag for indicating that memory copying processing for making the stored contents of the memory unit of the self system with stored contents of the memory unit or units of the processing unit or units of the other system or systems coincide with each other is proceeding.

[0016] Thus, the memory read-out means designated by any of the processors or the copy processor register reads out all stored contents of the memory unit while the processing unit is effecting ordinary processing, and the copying means transfers the stored contents and copies of data to be stored into the memory unit from the processor or any of the peripheral equipment or equipments in the same order as the order of accesses to the memory unit to the memory unit or units of the other processing unit or units. Then, after all stored contents of the memory unit are read out by the memory read-out means, contents of the cache memory are written back into the memory unit by the processor, and the thus written back contents of the cache memory are transferred to the memory unit or units of the other processing unit or units by the copying means. Coincidence of the stored contents of the memory units of the plurality of processing units is achieved thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a block diagram of a duplicated computer system to which the present invention is applied;

[0018]FIG. 2 is a block diagram of a processor-memory interface of the duplicated computer system of FIG. 1 showing a first preferred embodiment of the present invention;

[0019]FIG. 3 is a block diagram of a memory copy control circuit of the processor-memory interface of FIG. 2;

[0020]FIG. 4 is a block diagram of a DSBA of the duplicated computer system of FIG. 1;

[0021]FIG. 5 is a diagrammatic view showing a detailed construction of a copy transfer register of the DSBA of FIG. 4;

[0022]FIG. 6 is a diagrammatic view illustrating an operation of the duplicated computer system of FIG. 1;

[0023]FIG. 7 is a similar view but illustrating another operation of the duplicated computer system of FIG. 1;

[0024]FIG. 8 is a table illustrating operation of the duplicated computer system of FIG. 1;

[0025]FIG. 9 is a diagrammatic view illustrating a further operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 2 is employed;

[0026]FIG. 10 is a similar view but illustrating a still further operation of the duplicated computer system of FIG. 1;

[0027]FIG. 11 is a similar view but illustrating a yet further operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 2 is employed;

[0028]FIG. 12 is a sequential diagram illustrating a fault recovering operation of the duplicated computer system of FIG. 1;

[0029]FIG. 13 is a flow chart illustrating details of a memory copying operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 2 is employed;

[0030]FIG. 14 is a block diagram of another processor-memory interface of the duplicated computer system of FIG. 1 showing a second preferred embodiment of the present invention;

[0031]FIG. 15 is a block diagram of a memory copy control circuit of the processor-memory interface of FIG. 14;

[0032]FIG. 16 is a block diagram illustrating an operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 14 is employed;

[0033]FIG. 17 is a similar view but illustrating another operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 14 is employed; and

[0034]FIG. 18 is a flow chart illustrating details of a memory copying operation of the duplicated computer system of FIG. 1 where the processor-memory interface of FIG. 14 is employed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In the following, preferred embodiments of the present invention will be described with reference to the drawings.

First Embodiment

[0036]FIG. 1 is a block diagram showing a duplicated computer system to which the present invention is applied. The duplicated computer system includes an A system CPU block 10 a and a B system CPU block 10 b which perform predetermined operation processing, an A system peripheral equipment block 100 a including at least one peripheral equipment 150 a, and a B system peripheral equipment block 100 b including at least one peripheral equipment 150 b. The CPU blocks of the two systems and the A system peripheral equipment block 100 a are connected to each other by a duplicated bus 110 a, and the CPU blocks of the two systems and the B system peripheral equipment block 100 b are connected to each other by another duplicated bus 110 b. Further, the two system peripheral equipment blocks and a terminal equipment 180 are connected to each other by a terminal connection apparatus 170.

[0037] Components of the two systems which correspond to each other (which are denoted by like reference numerals with different suffixes annexed) have same functions, and the two systems have a same construction.

[0038] The A system CPU block 10 a includes at least a processor group 20 a including a plurality of processors which perform single or multiple processor operations, a cache group 22 a including caches individually connected to the processors of the processor group 20 a, a memory 30 a, a ROM 35 a in which at least a startup processing program and a fault recovery program are built in, a processor-memory interface 40 a called PMI, an inter-system interface 50 a called PXI, a plurality of duplicated bus control apparatus 70 a and 80 a called DSBA, and a system bus 60 a for connecting the PMI 40 a and the DSBAs 70 a and 80 a to each other. Similarly, the B system CPU block 10 b includes at least a processor group 20 b composed of the number of processors equal to the number of the processors of the processor group 20 a of the A system CPU block 10 a, a cache group 22 b including caches individually connected to the processors of the processor group 20 b, a memory 30 b, a ROM 35 b, a processor-memory interface 40 b called PMI, an inter-system interface 50 b called PXI, a plurality of duplicated bus control apparatus 70 b and 80 b called DSBA, and a system bus 60 b for connecting the PMI 40 b and the DSBAs 70 b and 80 b.

[0039] While the ROM 35 a and the ROM 35 b are connected to the system bus 60 a and the system bus 60 b, respectively, they may be connected, for example, to the PMIs 40 a and 40 b or the PXIs 50 a and 50 b, respectively.

[0040] The A system CPU block 10 a further includes a clock apparatus 90 a for supplying a clock signal having the same frequency and the same phase as those of the B system CPU block 10 b to the A system CPU block 10 a and the B system CPU block 10 b. Similarly, the B system CPU block 10 b further includes a clock apparatus 90 b for supplying a clock signal having the same frequency and the same phase as those of the A system CPU block 10 a to the A system CPU block 10 a and the B system CPU block 10 b. Normally, only a clock signal supplied from one of the two clock apparatus is used commonly by the A system CPU block 10 a and the B system CPU block 10 b.

[0041] The A system CPU block 10 a and the B system CPU block 10 b perform the same operation, that is, synchronous operations in accordance with a period of a clock signal supplied thereto from one of the clock apparatus 90 a and 90 b. In short, the A system CPU block 10 a and the B system CPU block 10 b perform duplicated system operations in which the same operation processing is performed.

[0042] The A system CPU block 10 a has at least three states of an on-line state, a disconnected state and a copying state, and one of the states is set to a state register 55 a of the PXI 50 a. The processor group 20 a and the processor 20 b can perform reading out from and writing into the state register 55 a. Also the B system CPU block 10 b is constructed in a similar manner. In the following, the three states will be described.

[0043] The on-line state is a state in which ordinary operation processing is performed, and when both of the A system CPU block 10 a and the B system CPU block 10 b are in the on-line state, the two system CPU blocks are performing synchronous operations.

[0044] The disconnected state is a state wherein transmission to the duplicated bus 110 a and the duplicated bus 110 b and reception from the duplicated bus 110 a and the duplicated bus 110 b are inhibited, that is, a state wherein the A system CPU block 10 a or the B system CPU block 10 b is logically disconnected from the duplicated computer system.

[0045] The copying state is a state wherein a copy of memory contents transmitted from the other system CPU block is received in order to make the memory of the self system CPU block coincident with the memory of the other system CPU block.

[0046] The A system peripheral equipment block 100 a includes at least a peripheral equipment control apparatus 140 a called IOA for controlling the peripheral equipment 150 a, another peripheral equipment control apparatus 141 a called IOA for controlling the terminal connection apparatus 170, an I/O bus 130 a for connecting one or a plurality of IOAs 140 a, an I/O bus control apparatus 120 a called MBA having a function of connecting the I/O bus 130 a and the duplicated bus 110 a to each other to arbitrate accessing to the I/O bus 130 a, and a clock apparatus 160 a for supplying a clock signal to the A system peripheral equipment block 100 a.

[0047] Similarly, the B system peripheral equipment block 100 b includes at least a peripheral equipment control apparatus 140 b called IOA for controlling the peripheral equipment 150 b, another peripheral equipment control apparatus 141 b called IOA for controlling the terminal connection apparatus 170, an I/O bus 130 b for connecting one or a plurality of IOAs 140 b, an I/O bus control apparatus 120 b called MBA having a function of connecting the I/O bus 130 b and the duplicated bus 110 b to each other to arbitrate accessing to the I/O bus 130 b, and a clock apparatus 160 b for supplying a clock signal to the B system peripheral equipment block 100 b.

[0048] The terminal equipment 180 can perform, for example, a maintenance operation for the duplicated computer system as an operator operates the terminal equipment 180.

[0049] If a user manually operates the terminal equipment 180 to request the duplicated computer system to perform predetermined processing, then the duplicated computer system executes the requested processing simultaneously by both of the A system CPU block 10 a and the B system CPU block 10 b. Consequently, even if a failure occurs with one of the CPU blocks to stop its processing, processing is executed continuously by the other CPU block, and accordingly, the requested processing is performed.

[0050] Subsequently, a construction and operation of the PMI 40 a which is a principal element of the present invention will be described with reference to FIG. 2. It is to be noted that also the PMI 40 b is constructed and operates in a similar manner.

[0051] The PMI 40 a includes a processor interface 410 a which communicates data with the processor group 20 a, a memory interface 420 a for effecting reading out of and writing into the memory 30 a, a system bus interface 490 a for communicating data with the DSBAs 70 a and 80 a, and various logical operation elements.

[0052] The processor interface 410 a requests the memory interface 420 a for memory accessing in response to a memory access from the processor group 20 a. Similarly, the system bus interface 490 a requests the memory interface 420 a for memory accessing in response to a memory access from the DSBA 70 a or the DSBA 80 a. The memory interface 420 a arbitrates the memory access requests from the processor interface 410 a and the system bus interface 490 a to execute desired memory accessing. The maximum data length accessed by a single memory accessing operation is equal to the data line length of the cache group 22 a. A data line is composed of data of a plurality of bytes and allocated to successive address regions. It is to be noted that a memory access from the DSBA 70 a or the DSBA 80 a is produced by data transfer from the peripheral equipment 150 a or 150 b, that is, so-called DMA (Dynamic Memory Access). Further, the processor interface 410 a requests the system bus interface 490 a for PIO accessing in response to a read or write access, that is, a so-called PIO (Peripheral Input/Output) access of any of various registers provided in the components connected to the system bus 60 a from the processor group 20 a, and the system bus interface 490 a executes desired PIO accessing to any of the various registers of the components connected to the system bus 60 a in response to such PIO accessing request.

[0053] A further detailed construction of the memory interface 420 a will be described.

[0054] The memory interface 420 a includes a memory access control circuit 421 a, an RAS/CAS production circuit 422 a for producing a row address and a column address of the memory 30 a, an ECC check correction circuit 423 a for detecting and correcting a bit error of read data read out from the memory 30 a using an ECC (Error Correcting Code), an ECC production circuit 424 a for producing an ECC for write data to be written into the memory 30 a, and various logic operation devices.

[0055] Subsequently, a basic operation of the memory interface 420 a will be described.

[0056] If the processor interface 410 a outputs a memory access request signal 413 a and an access type code signal 414 a, which indicates read/write and a data length, to the memory access control circuit 421 a and similarly the system bus interface 490 a outputs a memory access request signal 493 a and an access code type signal 494 a to the memory access control circuit 421 a, then the memory access control circuit 421 a refers to those signals and selects one of the memory accesses from the processor interface 410 a and the system bus interface 490 a based on a preferential order set in advance, and then outputs a access acceptance signal 425 a or 426 a to the interface which is the access source of the selected memory access. Further, a multiplexer 427 a is changed over so that a selected one of memory access addresses 411 a and 491 a outputted from the processor interface 410 a and the system bus interface 490 a is transmitted to the RAS/CAS production circuit 422 a, and a row address and a column address produced by the RAS/CAS production circuit 422 a are transmitted to the memory 30 a via a buffer 431 a.

[0057] Further, the memory access control circuit 421 a changes over, if the selected memory access is a write address, a multiplexer 429 a to transmit a selected one of memory write data 412 a and 492 a outputted from the processor interface 410 a and the system bus interface 490 a to the memory via a buffer 433 a together with the ECC produced by the ECC production circuit 424 a. Or, if the selected memory access is a read access, then the memory access control circuit 421 a transmits read data read out from the memory 30 a via a buffer 432 a to the ECC check correction circuit 423 a, and changes over a demultiplexer 428 a so that read data after ECC checking and correction have been performed are transmitted to a selected one of the processor interface 410 a and the system bus interface 490 a.

[0058] Subsequently, components for memory copying will be described.

[0059] The memory interface 420 a further includes, in order to perform so-called memory copying wherein data stored in the memory 30 a are copied into the memory 30 b of the B system CPU block 10 b to make the memory 30 b coincident with the memory 30 a, an address queue memory 451 a for storing an access address selected by the multiplexer 427 a, a data queue memory 452 a for storing write data selected by the multiplexer 429 a and read data outputted from the ECC check correction circuit 423 a, a multiplexer 453 a for selecting write data and read data to be stored into the data queue memory 452 a, and a memory copy control circuit 440 a for performing reading out of the memory 30 a and controlling the address queue memory 451 a and the data queue memory 452 a. It is to be noted that, since the A system CPU block 10 a executes memory copying in parallel to ordinary processing, during copying, not only data stored in the memory 30 a are copied, but also write data to be written into the memory 30 a are copied in order to maintain the coincidence between the memory 30 a and the memory 30 b which always varies by ordinary processing.

[0060]FIG. 3 is a block diagram of the memory copy control circuit 440 a.

[0061] The memory copy control circuit 440 a includes a copy mode flag 444 a indicating that memory copying is proceeding, a copy task flag 448 a indicating that the processor is performing reading out of the memory 30 a, that is, the processor is performing copying of stored contents of the memory 30 a in order to perform memory copying, a copy processor register 449 a indicating the number of a processor which executes memory reading out for memory copying, and a copy control section 441 a for controlling the address queue memory 451 a and the data queue memory 452 a.

[0062] The copy mode flag 444 a, copy task flag 448 a and copy processor register 449 a can be written/read out by the processor group 20 a.

[0063] The copy control section 441 a refers to the copy mode flag 444 a, the access type code signals 414 a and 494 a and the access acceptance signals 425 a and 426 a and, if the copy mode flag 444 a is set to 1, then the copy control section 441 a stores, in response to the access acceptance signal 425 a to a memory write request from the processor interface 410 a, a write address outputted from the multiplexer 427 a and write data outputted from the multiplexer 429 a into the address queue memory 451 a and the data queue memory 452 a, respectively. Further, in response to the access acceptance signal 426 a to a memory write request from the system bus interface 490 a, the copy control section 441 a stores a write address outputted from the multiplexer 427 a and write data outputted from the multiplexer 429 a into the address queue memory 451 a and the data queue memory 452 a, respectively.

[0064] On the other hand, if the copy task flag 448 a is set to 1, then the copy control section 441 a stores, in response to the access acceptance signal 425 a to a memory write request from the processor interface 410 a, a write address outputted from the multiplexer 427 a and write data outputted from the multiplexer 429 a into the address queue memory 451 a and the data queue memory 452 a, respectively. Further, in response to the access acceptance signal 425 a to a memory read request from the processor interface 410 a whose access source is a processor designated by the copy processor register 449 a, the copy control section 441 a stores a read address outputted from the multiplexer 427 a and read data outputted from the ECC check correction circuit 423 a into the address queue memory 451 a and the data queue memory 452 a, respectively. Furthermore, in response to the access acceptance signal 426 a to a memory write request from the system bus interface 490 a, the copy control section 441 a stores a write address outputted from the multiplexer 427 a and write data outputted from the multiplexer 429 a into the address queue memory 451 a and the data queue memory 452 a, respectively. It is to be noted that locations of the address queue memory 451 a and the data queue memory 452 a into which an address and data are to be stored are designated by a pointer 460 a.

[0065] The copy control section 441 a further outputs to the system bus interface 490 a, after memory access addresses and data are stored into the address queue memory 451 a and the data queue memory 452 a, respectively, a copy transmission request signal 458 a and a pointer 459 a representative of a position at which an address and data to be transferred are stored in order to transfer the data to the memory 30 b of the B system CPU block 10 b in the order in which they have been stored. The system bus interface 490 a reads out an address and data indicated by the pointer 459 a from the address queue memory 451 a and the data queue memory 452 a, respectively, in response to the copy transmission request signal 458 a, adds an identifier representing copying to the thus read out address and data and transmits them to the system bus 60 a. This identifier can be realized, for example, by allocating one of patterns of type codes representative of kinds of bus accesses in the system bus 60 a. The system bus interface 490 a outputs a copy transmission end signal 495 a to the copy control section 441 a after copying transmission to the system bus 60 a is completed. When the copy transmission end signal 495 a is received, the copy control section 441 a requests the system bus interface 490 a for next copying transmission by a next operation similar to that described above.

[0066] If the address queue memory 451 a and the data queue memory 452 a become full, then the copy control section 441 a outputs a BUSY signal 457 a to the memory access control circuit 421 a, and in response to the BUSY signal 457 a, the memory access control circuit 421 a inhibits memory accessing which requires copying. For example, when the copy mode flag 444 a is set to 1 and the copy task flag 448 a is set to 0, while the BUSY signal 457 a is outputted, a write access by the processor and a write access by DMA are rejected, but when the copy task flag 448 a is set to 1, while the BUSY signal 457 a is outputted, read and write accesses by the processor and a write access by DMA are rejected. Failure in memory copying is prevented thereby.

[0067] Subsequently, a construction and operation of the DSBAs 70 a, 80 a, 70 b and 80 b will be described with reference to FIG. 4.

[0068] The DSBA 70 a includes a PIO queue memory 711 a for storing a PIO read address and PIO write address/data received from the system bus 60 a together with an access type code corresponding to them, a DMA queue memory 712 a for storing DMA read data received from the system bus 60 a together with a corresponding access type code, a copy queue memory 713 a for storing copy address/data received from the system bus 60 a together with a corresponding access type code, a PIO queue memory 721 a for storing PIO read data received from the duplicated bus 110 a together with a corresponding access type code, a DMA queue memory 722 a for storing a DMA read address and DMA write address/data received from the duplicated bus 110 a together with an access type code corresponding to them, a copy queue memory 723 a for storing copy address/data received from the duplicated bus 110 a together with a corresponding access type code, a system bus access control circuit 731 a for controlling communication of the system bus 60 a, a duplicated bus control circuit 741 a for controlling the duplicated bus 110 a, a base address register 751 a for indicating an I/O address region of the A system peripheral equipment block connected to the DSBA 70 a via the duplicated bus 110 a, a copy transfer register 753 a for indicating that copy address/data from the PMI 40 a are to be accepted, a mode flag 752 a for indicating a mode of the DSBA 70 a, and various logic operation devices. Also the DSBAs 80 a, 70 b and 80 b have a similar construction.

[0069] It is to be noted that the system bus 60 a and the duplicated bus 110 a may transmit an address and data in time division using the same signal line or using separate signal lines. Further, the base address register 751 a, copy transfer register 753 a and mode flag 752 a can be written/read out by the processor group 20 a.

[0070] The system bus access control circuit 731 a compares an address outputted to the system bus 60 a by the PMI 40 a with a value of the base address register 751 a, and if the address outputted is within the I/O address region of the A system peripheral equipment block connected to the DSBA 70 a, then the access is received by the system bus access control circuit 731 a via a buffer 732 a and stored into a predetermined queue memory by a demultiplexer 734 a. However, reception of copy address/data is defined by setting of the copy transfer register 753 a.

[0071] Referring to FIG. 5, the copy transfer register 753 a includes a COPY flag 7531 a for indicating that copy address/data from the PMI 40 a are to be accepted, a CAD1 flag 7532 a and a CAD2 flag 7533 a for indicating values of the lowest two bits of a copy address to be accepted, and a CAE1 flag 7534 a and a CAE2 flag 7535 a for indicating that the CAD1 flag 7532 a and the CAD2 flag 7533 a are valid, respectively. For example, if the COPY flag 7531 a is set to 1, the CAE1 flag 7534 a to 0 and the CAE2 flag 7535 a to 1, then the system bus access control circuit 731 a accepts copy address/data from the PMI 40 a only if the value of the lowest one bit of the address is equal to a value set to the CAD1 flag 7532 a, or if the COPY flag 7531 a is set to 1, the CAE1 flag 7534 a to 1 and CAE2 flag 7535 a to 1, then the system bus access control circuit 731 a accepts copy address/data from the PMI 40 a only if the values of the lowest two bits of the address are equal to values set to the CAD1 flag 7532 a and the CAD2 flag 7533 a. The copy transfer register 753 a stores copy addresses/data accepted in this manner into the copy queue memory 713 a selected by the demultiplexer 734 a.

[0072] The system bus access control circuit 731 a further selects addresses, data and access type codes stored in one of the PIO queue memory 721 a, DMA queue memory 722 a and copy queue memory 723 a in accordance with a predetermined preferential order by means of a multiplexer 735 a and outputs them to the system bus 60 a via a buffer 733 a.

[0073] The DSBA 70 a can be set to one of a primary mode and a secondary mode by the mode flag 752 a. The DSBA in the primary mode outputs address/data and a control signal to a duplicated bus, but the DSBA in the secondary mode inhibits outputting of address/data and a control signal to the duplicated bus. This prevents collision of outputting from the A system CPU block 10 a and the B system CPU block 10 b to the duplicated bus 110 a or the duplicated bus 10 b. Accordingly, one of the DSBA 70 a and the DSBA 70 b is set to the primary mode while the other is set to the secondary mode, and one of the DSBA 80 a and the DSBA 80 b is set to the primary mode while the other is set to the secondary mode.

[0074] The duplicated bus control circuit 741 a receives an address, data and an access type code outputted to the duplicated bus 110 a by the MBA 120 a via a buffer 743 a and stores them into a predetermined queue memory by means of a demultiplexer 745 a.

[0075] The duplicated bus control circuit 741 a further selects addresses, data and access type codes stored in one of the PIO queue memory 711 a, DMA queue memory 712 a and copy queue memory 713 a in accordance with a preferential order set in advance by means of a multiplexer 744 a and outputs them to the duplicated bus 110 a via a buffer 742 a.

[0076] The duplicated bus control circuit 741 a controls a duplicated bus in accordance with a state of the A system CPU block 10 a indicated by the state register 55 a of the PXI 50 a and a mode indicated by the mode flag 752 a. In particular, in an on-line state and the primary mode, the duplicated bus control circuit 741 a receives a control signal, an address, data and an access type code from the duplicated bus 110 a and transmits the control signal, address, data and access type code to the duplicated bus 110 a via buffers 747 a and 742 a.

[0077] In an on-line state and the secondary mode, the duplicated bus control circuit 741 a receives a control signal, an address, data and an access type code from the duplicated bus 110 a via buffers 746 a and 743 a. However, the duplicated bus control circuit 741 a inhibits outputting of the control signal, address, data and access type code to the duplicated bus 110 a by normally keeping the buffers 747 a and 742 a in a high impedance state. However, the duplicated bus control circuit 741 a presumably regards that it has outputted the control signal, address, data and access type code to the duplicated bus 110 a.

[0078] In a copying state, all DSBAs are set to the secondary mode, and the bus access type code of the duplicated bus 110 a is supervised so that only memory copy address/data and a type code transmitted from the other system CPU block are received while a DMA write access transmitted from the MBA 120 a is not received. Outputting of a control signal, an address, data and an access type code to the duplicated bus 110 a is inhibited by normally keeping the buffers 747 a and 742 a in a high impedance state.

[0079] In a disconnected state, a control signal, an address, data and an access type code received from the duplicated bus 110 a are abandoned whereas outputting of a control signal, an address, data and an access type code to the duplicated bus 110 a is inhibited by normally keeping the buffers 747 a and 742 a in a high impedance state.

[0080] Subsequently, data transfer, that is, so-called DMA (Dynamic Memory Access), between the memory 30 a or 30 b and the peripheral equipment 150 a or 150 b when the A system CPU block 10 a and the B system CPU block 10 b are in an on-line state, that is, are operating in synchronism with each other, will be described with reference to FIGS. 1, 6 and 7.

[0081] When the A system CPU block 10 a and the B system CPU block 10 b are in an on-line state, the DSBAs 70 a and 80 b are set to the primary mode while the DSBAs 70 b and 80 a are set to the secondary mode.

[0082] DMA is executed by the IOAs 140 a and 140 b. Since memory accessing by DMA is executed quite independently of memory accessing by any processor, contention between a memory access by DMA and another memory access by a processor occurs in the PMI 40 a and the PMI 40 b. However, the memory interfaces 420 a and 420 b arbitrate the memory accesses so that desired memory accessing may be executed as described hereinabove.

[0083]FIG. 6 illustrates DMAs from the peripheral equipment 150 a to the memory 30 a and the memory 30 b. The IOA 140 a transmits data read out from the peripheral equipment 150 a to the MBA 120 a via the I/O bus 130 a. The MBA 120 a outputs the thus received data to the duplicated bus 110 a. The DSBA 70 a and the DSBA 70 b simultaneously receive the data outputted to the duplicated bus 110 a and simultaneously transmits the data to the PMI 40 a and the PMI 40 b via the system bus 60 a and the system bus 60 b, respectively. The PMI 40 a and the PMI 40 b write the received data simultaneously into the memory 30 a and the memory 30 b, respectively. DMAs from the peripheral equipment 150 b to the memory 30 a and the memory 30 b proceed in a similar manner.

[0084]FIG. 7 illustrates DMAS from the memory 30 a and the memory 30 b to the peripheral equipment 150 a. The PMI 40 a and the PMI 40 b transmit data read out simultaneously from the memory 30 a and the memory 30 b to the DSBA 70 a and the DSBA 70 b via the system bus 60 a and the system bus 60 b, respectively. The DSBA 70 a and the DSBA 70 b transmit the thus received data to the MBA 120 a via the duplicated bus 110 a. However, actually the data are outputted to the duplicated bus 110 a only from the DSBA 70 a which is in the primary mode while the DSBA 70 b which is in the secondary mode does not output the data. This prevents a signal of the duplicated bus 110 a from being rendered unstable by simultaneous driving of the duplicated bus 110 a by the DSBA 70 a and the DSBA 70 b. The MBA 120 a transmits the thus received data to the IOA 140 a via the I/O bus 130 a, and the IOA 140 a transmits the thus received data to the peripheral equipment 150 a. DMAs also from the memory 30 a and the memory 30 b to the peripheral equipment 150 b proceed in a similar manner.

[0085] Subsequently, copy transfer when the A system CPU block 10 a is in an on-line state and the B system CPU block 10 b is in a copying condition, that is, when memory copying from the memory 30 a to the memory 30 b is proceeding, will be described with reference to FIGS. 1, 8, 9, 10 and 11.

[0086] When the A system CPU block 10 a is in an on-line state and the B system CPU block 10 b is in a copying state, the DSBAs 70 a and 80 a are set to the primary mode and the DSBAs 70 b and 80 b are set to the secondary mode. Further, the copy transfer registers of the DSBAs 70 a and 80 a are set in such a manner as illustrated in FIG. 8 so that a copy whose address is an even number is transferred via the duplicated bus 110 a by the DSBA 70 a whereas another copy whose address is an odd number is transferred via the duplicated bus 110 b by the DSBA 80 a.

[0087]FIG. 9 illustrates copy transfer of contents of the memory 30 a read out by a processor in the processor group 20 a designated by the copy processor register 449 a.

[0088] The PMI 40 a transmits a copy of contents of the memory 30 a read out by the processor designated by the copy processor register 449 a to the DSBA 70 a or the DSBA 80 a via the system bus 60 a. The DSBA 70 a or the DSBA 80 a transmits the received copy to the DSBA 70 b or the DSBA 80 b via the duplicated bus 110 a or the duplicated bus 110 b. The DSBA 70 b or the DSBA 80 b transmits the received copy to the PMI 40 b via the system bus 60 b. The PMI 40 b writes the received copy into the memory 30 b.

[0089]FIG. 10 illustrates copy transfer of a write access from the processor group 20 a to the memory 30 a.

[0090] The PMI 40 a transmits a copy of a write access from the processor group 20 a to the memory 30 a to the DSBA 70 a or the DSBA 80 a via the system bus 60 a. The DSBA 70 a or the DSBA 80 b transmits the received copy to the DSBA 70 b or the DSBA 80 b via the duplicated bus 110 a or the duplicated bus 110 b. The DSBA 70 b or the DSBA 80 b transmits the received copy to the PMI 40 b via the system bus 60 b. The PMI 40 b writes the received copy into the memory 30 b.

[0091]FIG. 11 illustrates copy transfer of a DMA write access from the peripheral equipment 150 a to the memory 30 a.

[0092] If DMA write accessing is executed during execution of memory copying, then the memory coincidence is sometimes lost. This is because, when DMA write accessing is executed for a certain memory region as illustrated in FIG. 6, if the memory copy control circuit 440 a reads out the same memory region and transfers a copy of the memory region to the memory 30 b immediately before data are written into the memory 30 a and the memory 30 b by the DMA write accessing, then the memory region updated by the DMA writing is written back into the state prior to the updating by the copying from the memory 30 a, resulting in incoincidence between the regions of the memory 30 a and the memory 30 b. Accordingly, copy transfer of DMA write accessing is executed in the following manner by the memory copy control circuit 440 a to establish coincidence of the memories.

[0093] The IOA 140 a transmits data read out from the peripheral equipment 150 a to the MBA 120 a via the I/O bus 130 a, and the MBA 120 a outputs the received data to the duplicated bus l10 a. The DSBA 70 a receives the data outputted to the duplicated bus 110 a while the DSBA 70 b does not receive the data outputted to the duplicated bus 110 a. The DSBA 70 a transmits the received data to the PMI 40 a via the system bus 60 a. The PMI 40 a writes the received data into the memory 30 a and transmits a copy of the write access to the DSBA 70 a or the DSBA 80 a via the system bus 60 a. The DSBA 70 a or the DSBA 80 a transmits the received copy to the DSBA 70 b or the DSBA 80 b via the duplicated bus 110 a or the duplicated bus 10 b. The DSBA 70 b or the DSBA 80 b transmits the received copy to the PMI 40 b via the system bus 60 b. The PMI 40 b writes the received copy into the memory 30 b.

[0094]FIG. 12 is a flow chart illustrating a fault recovering operation by execution of a fault recovery processing program when a failure occurs with the B system CPU block 10 b.

[0095] In FIG. 12, operation of the A system CPU block 10 a is illustrated on the left side and operation of the B system CPU block 10 b is illustrated on the right side. In the beginning, both of the two system CPU blocks are in an on-line state and are operating in synchronism with each other (step 1,200).

[0096] If occurrence of a failure in the B system CPU block 10 b is detected (step 1,201), then the B system CPU block 10 b reports the failure detection to the A system CPU block 10 a by means of the PXI 50 b (step 1,202). In response to the failure detection report, the A system CPU block 10 a requests the PXI 50 b of the B system CPU block 10 b for disconnection (step 1,203). The PXI 50 b sets the state register 55 b to a disconnection state when a failure is detected with the B system CPU 10 b and the disconnection request is received from the A system CPU block 10 a. After the disconnection state is entered, the DSBA 70 b and the DSBA 80 b inhibit communication of the duplicated buses 110 a and 110 b. Consequently, the B system CPU block 10 b is disconnected from the duplicated computer system (step 1,204), and the A system CPU block 10 a thereafter continues its processing solely. At this point of time, the duplicated system operation is disabled.

[0097] A user who performs maintenance and management of the system performs a work of exchanging the failed element of the B system CPU block 10 b such as, for example, a failed processor or memory for another device which has the same function and operates normally (step 1,205). After the work is completed, the B system CPU block 10 b is started by a manual operation of the terminal equipment 180 or the like (step 1,206).

[0098] It is to be noted that the B system CPU block 10 b may be started by a manual operation of the terminal equipment 180 or a program for executing processing corresponding to a starting operation may be executed in response to a manual operation of a starter switch which may be provided for the B system CPU block 10 b.

[0099] If the starting operation is performed, then the B system CPU block 10 b executes a self diagnosis program built in the ROM 35 b to check whether or not the B system CPU block 10 b is normal (step 1,207), and then executes an initialization program to initialize the cache group 22 b and the memory 30 b (step 1,208), whereafter it reports completion of the initialization to the A system CPU block 10 a (step 1,209).

[0100] In response to the initialization completion report, the A system CPU block 10 a sets the B system CPU block 10 b to a copying state (step 1,210) and performs memory copying (step 1,211). Then, after the memory copying is completed, the A system CPU block 10 a performs synchronization of the two system CPU blocks (step 1,212). This synchronization may be effected by simultaneous resetting of the two system CPU blocks or may be effected by responses (sent back simultaneously from the two system CPU blocks) when the two system CPU blocks read access a certain I/O register of the A system peripheral equipment block 100 a or the B system peripheral equipment block 100 b or else by transmitting timing signals for synchronization to each other.

[0101] After the synchronization of the two system CPU blocks is completed, the A system CPU block 10 a sets the B system CPU block 10 b to an on-line state to resume a duplicated system operation (step 1,213).

[0102]FIG. 13 is a flow chart illustrating contents of operation of memory copying. A sequence of steps of operation for memory copying is performed by a designated one processor in the processor groups of the CPU block which is in an on-line state.

[0103] First, the designated processor sets the copy mode flag 444 a to 1 (step 1,301).

[0104] Then, the designated processor sets the copy task flag 448 a to 1 (step 1,302).

[0105] Then, the designated processor flushes the caches in a fixed memory region (step 1,303). This is performed in order to have memory read accessing performed by the processor with certainty.

[0106] Thereafter, the designated processor executes a load instruction to the caches in the memory region for which flushing has been executed (step 1,304). The memory region was cache flushed in step 1,303, and consequently, if the load instruction is executed, then a cache miss occurs and memory reading is executed. Stored contents of the memory read out by the memory reading are copied by the memory copy control circuit 440 a and transferred to a memory of the other system.

[0107] Subsequently, the designated processor executes cache flushing again to the memory region for which the load instruction has been executed (step 1,305). This is performed in order to recover the cache consistency of the memory region for which the load instruction has been performed independently of ordinary operation processing.

[0108] It is to be noted that the steps 1,303, 1,304 and 1,305 may be performed in units of a memory region of, for example, 4 kilobytes or in units of a memory space of a memory region having an equal size to that of a cache line.

[0109] Subsequently, the designated processor sets the copy task flag 448 a to 0 (step 1,306).

[0110] Then, the designated processor discriminates whether or not all of the memory regions have been copied (step 1,307). If all of the memory regions have not been copied, then in order to minimize an influence on ordinary operation processing, a predetermined interval of time is placed (step 1,308), and then the operations in steps 1,302 through 1,306 are executed for a next address region. If all of the memory regions have been copied, then all caches of the processor group are flushed and data present only in the caches are copied to establish the coincidence of all of the memory regions including the caches (step 1,309). The memory copying is completed thereby.

[0111] While, in the foregoing description, reading out of stored contents of the memory 30 a is performed by one of the processors of the processor group 20 a in order to copy all of the stored contents of the memory 30 a and a DMA write access is normally copied in order to assure the data coincidence in memory copying, as another form, it should be noted that reading out of the stored contents of the memory 30 a is performed by a memory copy control circuit for exclusive use provided in the processor-memory interface 40 a to reduce the burden to the processors, or only a DMA write access which is determined to have the possibility that it may cause a loss of data coincidence is copied from among DMA write accesses generated during memory copying to reduce the burden to a duplicated bus which serves as a transfer path for copy data or DMAS.

Second Embodiment

[0112] In particular, as a second embodiment, a form wherein reading out of stored contends of the memory 30 a is performed by a memory copy control circuit for exclusive use provided in the processor-memory interface 40 a and any DMA write access is normally copied, another form wherein reading out of stored contents of the memory 30 a is performed by a processor and only any DMA write access which is determined to have the possibility that it may cause loss of data coincidence is copied or a further form wherein reading out of stored contents of the memory 30 a is performed by a memory copy control circuit for exclusive use provided in the processor-memory interface 40 a and only any DMA write access which is determined to have the possibility that it may cause loss of data coincidence is copied, is possible. Here, while, for the convenience of description, the form wherein reading out of stored contents of the memory 30 a is performed by a memory copy control circuit for exclusive use provided in the processor-memory interface 40 a and only any DMA write access which is determined to have the possibility that it may cause loss of data coincidence is described as the second embodiment, the form wherein reading out of stored contends of the memory 30 a is performed by a memory copy control circuit for exclusive use provided in the processor-memory interface 40 a and a DMA write access is normally copied or the form wherein reading out of stored contents of the memory 30 a is performed by a processor and only any DMA write access which is determined to have the possibility that it may cause loss of data coincidence is copied can be realized readily from the first embodiment described hereinabove and the second embodiment described below.

[0113] In the following, the second embodiment of the present invention will be described with reference to FIGS. 14, 15, 16 and 17. It is to be noted that a duplicated computer system, DSBAs, a synchronizing operation of an A system CPU block and a B system CPU block and a fault recovering operation are similar to those of the first embodiment, and FIGS. 1, 4, 5, 6, 7, 8, 10 and 12 are applied also to the second embodiment.

[0114]FIG. 14 shows a construction of the PMI 40 a in the second embodiment. The PMI 40 a includes a processor interface 1410 a for communicating data with the processor group 20 a, a memory interface 1420 a for reading out of and writing into the memory 30 a, a system bus interface 1490 a for communicating data with the DSBAs 70 a and 80 a via the system bus 60 a, and various logical operation devices.

[0115] The processor interface 1410 a requests the memory interface 1420 a for memory accessing in response to a memory access from the processor group 20 a, and the system bus interface 1490 a requests the memory interface 1420 a for memory accessing in response to a memory access from the DSBA 70 a or the DSBA 80 a. The memory interface 1420 a arbitrates memory access requests from the processor interface 1410 a and the system bus interface 1490 a to execute desired memory accessing. The maximum data length accessed by a single memory accessing operation is equal to the data line length of the cache group 22 a. A data line includes data of a plurality of bytes and is allocated to successive address regions. It is to be noted that a memory access from the DSBA 70 a or the DSBA 80 a is produced by data transfer from the peripheral equipment 150 a or 150 b, that is, so-called DMA (Dynamic Memory Access). Further, the processor interface 1410 a requests the system bus interface 1490 a for PIO accessing in response to a read or write access by the processor group 20 a to any of various registers provided in the components connected to the system bus 60 a, that is, so-called PIO (Peripheral Input/Output) access. The system bus interface 1490 a executes desired PIO accessing to any of the registers of the components connected to the system bus 60 a in response to the PIO access request.

[0116] A detailed construction of the memory interface 1420 a will be described. The memory interface 1420 a includes a memory access control circuit 1421 a, an RAS/CAS production circuit 1422 a for producing a row address and a column address of the memory 30 a, an ECC check correction circuit 1423 a for detecting and correcting a bit error of read data read out from the memory 30 a using an ECC (Error Correction Code), an ECC production circuit 1424 a for producing an ECC for write data to be written into the memory 30 a, and various logical operation devices. Subsequently, a basic operation of the memory interface 1420 a will be described.

[0117] If the processor interface 1410 a outputs a memory access request signal 1413 a and an access type code signal 1414 a representative of read/write and a data length to the memory access control circuit 1421 a and the system bus interface 1490 a similarly outputs a memory access request signal 1493 a and an access type code signal 1494 a to the memory access control circuit 1421 a, then the memory access control circuit 1421 a refers to those signals, and selects one of the memory accesses from the processor interface 1410 a and the system bus interface 1490 a based on a preferential order set in advance and outputs an access acceptance signal 1425 a or 1426 a to an interface which is an access source of the selected memory access. Further, the memory access control circuit 1421 a changes over a multiplexer 1427 a so that a selected one of a memory access address 1411 a outputted from the processor interface 1410 a, a memory access address 1491 a outputted from system bus interface 1490 a and a memory copy address 1454 a outputted from a memory copy control circuit 1440 a is transmitted to the RAS/CAS production circuit 1422 a, and a row address and a column address produced by the RAS/CAS production circuit 1422 a are transmitted to the memory 30 a via a buffer 1431 a.

[0118] Further, the memory access control circuit 1421 a changes over, if the selected memory access is a write access, a multiplexer 1429 a so that a selected one of memory write data 1412 a and 1492 a outputted from the processor interface 1410 a and the system bus interface 1490 a is transmitted to the memory via a buffer 1433 a together with an ECC produced by the ECC production circuit 1424 a. On the other hand, if the selected memory access is a read access, then read data read out from the memory 30 a via a buffer 1432 a are transmitted to the ECC check correction circuit 1423 a, and then a demultiplexer 1428 a is changed over so that read data after ECC checking and correction have been performed are transmitted to a selected one of the processor interface 1410 a and the system bus interface 1490 a.

[0119] Subsequently, components for memory copying will be described.

[0120] The memory interface 1420 a further includes, in order to perform so-called memory copying wherein data stored in the memory 30 a are copied to the memory 30 b of the B system CPU block 10 b to make the memory 30 b coincide with the memory 30 a, an address queue memory 1451 a for storing an access address selected by the multiplexer 1427 a, a data queue memory 1452 a for storing write data selected by the multiplexer 1429 a and read data outputted from the ECC check correction circuit 1423 a, a multiplexer 1453 a for selecting write data and read data to be stored into the data queue memory 1452 a, and a memory copy control circuit 1440 a for reading out the memory 30 a and controlling the address queue memory 1451 a and the data queue memory 1452 a. It is to be noted that, since the A system CPU block 10 a executes memory copying in parallel to ordinary processing, in order to maintain the coincidence between the memory 30 a and the memory 30 b which always varies by ordinary processing during memory copying, not only data stored in the memory 30 a are copied, but also write data to be written into the memory 30 a are copied.

[0121]FIG. 15 is a block diagram of the memory copy control circuit 1440 a in the second embodiment. The memory copy control circuit 1440 a includes a copy mode flag 1444 a for being used as a trigger to execution of memory copying, a copy address register 1443 a for indicting an address to be read out from the memory 30 a in order to copy data stored in the memory 30 a, a reading out section 1442 a for producing a read access to the address indicated by the copy address register 1443 a, timer means 1445 a for determining an interval of time after which a read access is to be produced by the reading out section 1442 a, a discrimination section 1446 a for discriminating that an abnormal overlap is produced by copying in the memory 30 b, and a copy control section 1441 a for controlling the address queue memory 1451 a and the data queue memory 1452 a.

[0122] The copy mode flag 1444 a and the copy address register 1443 a can be written/read out by the processor group 20 a. Further, the copy address register 1443 a is outputted as the memory copy address 1454 a to the multiplexer 1427 a.

[0123] When the copy mode flag 1444 a is set to 1 and a value other than 0 is placed in the copy address register 1443 a, the reading out section 1442 a outputs a memory access request signal 1455 a to the memory access control circuit 1421 a. The memory access control circuit 1421 a selects one of memory accesses from the processor interface 1410 a, the system bus interface 1490 a and the reading out section 1442 a in accordance with a preferential order set in advance. If the memory access from the reading out section 1442 a is selected, then the memory access control circuit 1421 a outputs an access acceptance signal 1456 a to the reading out section 1442 a and changes over the multiplexer 1427 a so that a memory copy address 1454 a which is a value of the copy address register 1443 a is transmitted to the RAS/CAS production circuit 1422 a to execute memory read accessing. The read data length in this instance is one line.

[0124] The reading out section 1442 a decrements, in response to the access acceptance signal 1456 a, the value of the copy address register 1443 a by one line and sets it as an address of a line to be read out subsequently, and then starts the timer means 1445 a. The timer means 1445 a has a function of measuring the time and notifies the reading out section 1442 a of an end of waiting when a waiting time set in advance elapses since the time of starting. Setting of the waiting time may be performed by a writing operation into a register provided in the timer means 1445 a.

[0125] In response to the waiting end notification from the timer means 1445 a, the reading out section 1442 a outputs a memory access request signal 1455 a to the memory access control circuit 1421 a again.

[0126] The operation described above is repetitively executed until the copy mode flag 1444 a is set to 0 or the value of the copy address register 1443 a becomes equal to 0. It is to be noted that the preferential order number of a memory access by the reading out section 1442 a should preferably be set to the lowest order number so that memory accessing by the processor group 20 a which is performing ordinary processing may not be obstructed.

[0127] The discrimination section 1446 a refers to the value of the copy address register 1443 a, the value of the memory access address 1491 a from the system bus interface 1490 a and an access type code signal 1494 a from the system bus interface 1490 a, and if the access type code signal 1494 a indicates memory write and the value of the memory access address 1491 a is higher than the value of the copy address register 1443 a but lower than the value of the copy address register 1443 a+a constant, then it is determined that a copy of the memory 30 a prior to updating by DMA writing is written into a memory region of the memory 30 b which has been updated by the same DMA writing and incoincidence between the memory 30 a and the memory 30 b results, and the discrimination section 1446 a outputs a DMA write copy request signal 1447 a to the copy control section 1441 a in order to request for memory accessing from the system bus interface 1490 a, that is, for copying of DMA write. It is to be noted that the value of the constant mentioned above is preferably set by a writing operation into a register provided in the discrimination section 1446. The value of the constant will be hereinafter described.

[0128] The copy control section 1441 a refers to the copy mode flag 1444 a, the access type code signals 1414 a, 1494 a and the access acceptance signal 1425 a, 1426 a and 1456 a, and if the copy mode flag 1444 a is set to 1, then the copy control section 1441 a stores a write address outputted from the multiplexer 1427 a and write data outputted from the multiplexer 1429 a into the address queue memory 1451 a and the data queue memory 1452 a, respectively, in response to an access acceptance signal 1425 a responding to the memory write request from the processor interface 1410 a. The copy control section 1441 a further stores, in response to another access acceptance signal 1456 a, a read address outputted from the multiplexer 1427 a and read data outputted from the ECC check correction circuit 1423 a into the address queue memory 1451 a and the data queue memory 1452 a, respectively. Furthermore, if the discrimination section 1446 a outputs a DMA write copy request signal 1447 a, the copy control section 1441 a stores a write address outputted from the multiplexer 1427 a and write data outputted from the multiplexer 1429 a into the address queue memory 1451 a and the data queue memory 1452 a, respectively, in response to an access acceptance signal 1426 a responding to the memory write signal from the system bus interface 1490 a. The locations for storing the address queue memory 1451 a and the data queue memory 1452 a are defined by a pointer 1460 a.

[0129] The copy control section 1441 a further outputs, after memory access addresses and data are stored into the address queue memory 1451 a and the data queue memory 1452 a, respectively, a copy transmission request signal 1458 a and a pointer 1459 a representative of a position into which an address and data to be transferred are stored to the system bus interface 1490 a in order to transfer the memory access addresses and the data in the order in which the memory access addresses and the data were stored. In response to the copy transmission request signal 1458 a, the system bus interface 1490 a reads out an address and data indicated by the pointer 1459 a from the address queue memory 1451 a and the data queue memory 1452 a, respectively, adds an identifier indicating that the address and the data are a copy and transmits the address and the data together with the identifier to the system bus 60 a. This identifier can be realized, for example, by allocating one of patterns of type codes representative of kinds of bus accesses in the system bus 60 a. After copy transmission to the system bus 60 a is completed, the system bus interface 1490 a outputs a copy transmission end signal 1495 a to the copy control section 1441 a. Upon reception of the copy transmission end signal 1495 a, the copy control section 1441 a requests the system bus interface 1490 a for next copy transmission.

[0130] Further, if the address queue memory 1451 a and the data queue memory 1452 a become full, the copy control section 1441 a outputs a BUSY signal 1457 a to the memory access control circuit 1421 a, and in response to the BUSY signal 1457 a, the memory access control circuit 1421 a inhibits memory accessing which requires copying. For example, while the BUSY signal 1457 a is outputted, a read access by the reading out section 1442 a, a write access by a processor and a write access by DMA are rejected. This prevents a miss of memory copying.

[0131] Subsequently, copy transfer when the A system CPU block 10 a is in an on-line state and the B system CPU block 10 b is in a copying state, that is, when memory copying from the memory 30 a to the memory 30 b is proceeding, will be described with reference to FIGS. 1, 16 and 17. When the A system CPU block 10 a is in an on-line state and the B system CPU block 10 b is in a copying state, the DSBAs 70 a and 80 a are set to the primary mode and the DSBAs 70 b and 80 b are set to the secondary mode. Further, the copy transfer registers of the DSBAs 70 a and 80 a are set in such a manner as illustrated in FIG. 8 similarly as in the first embodiment. Consequently, a copy whose address is an even number is transferred via the duplicated bus 110 a by the DSBA 70 a whereas a copy whose address is an odd number is transferred via the duplicated bus 110 b by the DSBA 80 a.

[0132]FIG. 16 illustrates copy transfer of contents of the memory 30 a read out by the memory copy control circuit 1440 a of the PMI 40 a.

[0133] The PMI 40 a transmits a copy of contents of the memory 30 a read out by the memory copy control circuit 1440 a to the DSBA 70 a or the DSBA 80 a via the system bus 60 a. The DSBA 70 a or the DSBA 80 a transmits the received copy to the DSBA 70 b or the DSBA 80 b via the duplicated bus 110 a or the duplicated bus 110 b. The DSBA 70 b or the DSBA 80 b transmits the received copy to the PMI 40 b via the system bus 60 b. The PMI 40 b writes the received copy into the memory 30 b.

[0134]FIG. 17 illustrates copy transfer of a DMA write access from the peripheral equipment 150 a to the memory 30 a.

[0135] If DMA write accessing is executed during execution of memory copying, then the memory coincidence is sometimes lost. This is because, when DMA write accessing is executed for a certain memory region as illustrated in FIG. 6, if the memory copy control circuit 1440 a reads out the same memory region and transfers a copy of the memory region to the memory 30 b immediately before data are written into the memory 30 a and the memory 30 b by the DMA write accessing, then the memory region updated by the DMA writing is written back into the state prior to the updating by the copying from the memory 30 a, resulting in incoincidence between the regions of the memory 30 a and the memory 30 b. Accordingly, when it is determined by the discrimination section 1446 a of the memory copy control circuit 1440 a that memory incoincidence mentioned hereinabove occurs, copy transfer of DMA write accessing is executed in such a manner as described below to establish coincidence of the memories. It is to be noted that the value of the constant of the discrimination section 1446 a is determined in the following manner. In particular, the value of the constant of the discrimination section 1446 a is set to a value equal to or higher than a maximum line number of one of copies of the memory 30 a read out by the memory copy control circuit 1440 a which has not been written into the memory 30 b as yet at an arbitrary point of time, that is, to a value equal to or higher than a maximum line number of copies present in the copy queue memories of the PMI or the DSBA and a copy being transmitted to a system bus or a duplicated bus. While this value depends upon the configuration of the system, the constant should preferably be set as low as possible.

[0136] The IOA 140 a transmits data read out from the peripheral equipment 150 a to the MBA 120 a via the I/O bus 130 a, and the MBA 120 a outputs the received data to the duplicated bus 110 a. The DSBA 70 a receives the data outputted to the duplicated bus 110 a while the DSBA 70 b does not receive the data outputted to the duplicated bus 110 a. The DSBA 70 a transmits the received data to the PMI 40 a via the system bus 60 a. The PMI 40 a writes the received data into the memory 30 a and transmits a copy of the write access to the DSBA 70 a or the DSBA 80 a via the system bus 60 a. The DSBA 70 a or the DSBA 80 a transmits the received copy to the DSBA 70 b or the DSBA 80 b via the duplicated bus 110 a or the duplicated bus 110 b. The DSBA 70 b or the DSBA 80 b transmits the received copy to the PMI 40 b via the system bus 60 b. The PMI 40 b writes the received copy into the memory 30 b. It is to be noted that copy transfer of the DMA write access is performed only when it is determined by the discrimination section 1446 a of the memory copy control circuit 1440 a that it is needed to copy the DMA write access, but in any other DMA write access, the copy transfer is executed in such a manner as illustrated in FIG. 6.

[0137] Copy transfer from the processor group 20 a to the memory 30 a in the second embodiment is performed by the operation described above with reference to FIG. 10 similarly as in the first embodiment.

[0138] A flow chart illustrating contents of operation of memory copying in the second embodiment is shown in FIG. 18. Setting/reading out operations for various registers are performed by a designated one of processors of the processor group of the CPU block which is in an on-line state.

[0139] First, the designated processor sets a last address of a memory region to the copy address register 1443 a (step 1,801).

[0140] Then, the copy mode flag 1444 a is set to 1 (step 1,802). Thereupon, reading out of memory contents by the address queue memory 1451 a and copy transfer of the thus read out memory contents are started. It is to be noted that the copy mode flag 1444 a is kept set to 1 until synchronization of the two CPU blocks is completed.

[0141] The designated processor periodically reads out the copy address register 1443 a and confirms whether or not the value of it is 0 (step 1,803). If the value of the copy address register 1443 a is 0, this signifies that copying of the entire memory space has been completed. However, at this point of time, the coincidence with the caches has not been established as yet.

[0142] Thus, all of the caches of the processor group are flushed and also data which are present only in the caches are copied to establish coincidence of all of the memory regions including the caches (step 1,804). Memory copying is completed thereby.

[0143] It is to be noted that, while, in the foregoing description, such a duplicated computer system as shown in FIG. 1 is described, the present invention can naturally be applied also to triplicated or more multiplexed computer systems.

[0144] As described in connection with the first embodiment above, by copying stored data read out from a memory unit by a processor and a copy of write data from the processor or a peripheral equipment to the memory unit in the same order as in the memory accessing into a memory of the other CPU block and flushing all caches after all data stored in the memory are copied, coincidence of the memories of the two system CPU blocks is realized. Consequently, during execution of memory copying, DMA between the peripheral equipment and the memories need not be inhibited different from the prior art.

[0145] Further, as described in connection with the second embodiment, by copying only that one of DMA write accesses produced during memory copying which is determined to have the possibility that it may cause loss of data coincidence, a load to a duplicated bus which serves as a transfer route for copy data or a DMA can be reduced.

[0146] Further, as described in connection with the second embodiment, if reading out of stored contents of a memory is performed by a memory copy control circuit for exclusive use provided in a possessor/memory interface, then only setting of registers in the beginning is required as pre-processing for memory copying. Consequently, the burden to the processor by pre-processing for memory copying can be reduced.

[0147] According to the present invention, in a computer system composed of a plurality of processing units and having a fault resisting function, stored data read out from a memory unit by a processor and copies of write data from the processor and a peripheral equipment or equipments to the memory unit are copied in the same order as that of the memory accesses into a memory or memories of the other CPU block or blocks, and after all data stored in the memory are copied, all caches are flushed thereby to realize coincidence of the memories of the two system CPU blocks. Consequently, during execution of memory copying, DMA between the peripheral equipment or equipments and the memories need not be inhibited different from the prior art. Accordingly, the processing performance during on-line maintenance can be improved comparing with that of the conventional system.

[0148] Further, by copying only that one of DMA write accesses produced during memory copying which is determined to have the possibility that it may cause loss of data coincidence, a load to a duplicated bus which serves as a transfer route for copy data or a DMA can be reduced. Consequently, the processing performance during on-line maintenance can be further improved.

[0149] Further, if reading out of stored contents of a memory is performed by a memory copy control circuit for exclusive use provided in a possessor/memory interface, then only setting of registers in the beginning is required as pre-processing for memory copying. Consequently, the burden to the processor by pre-processing for memory copying can be reduced, and the processing performance during on-line maintenance can be further improved. 

What is claimed:
 1. A data processor system comprising a plurality of processing units, each processing data using instructions and each including: a. a main memory which stores data and instructions; b. a controller having a controller memory; c. first signal lines coupling said controller to said main memory; d. second signal lines coupling said controller to said processor; and e. third signal lines coupling said controller to controllers in other of said plurality of processing units; f. said controller adapted to: i. select a memory access from said second signal lines or said third signal lines, ii. store data in the controller based on the selected memory access, iii. write data into said main memory based on said selected memory access, and iv. send the stored data to at least one controller in another of the plurality of processing units using the third signal lines.
 2. A data processor system according to claim 1 , wherein a memory access includes an address and data, said controller memory includes an address queue and a data queue and said controller storing said data and said address in said data queue and address queue respectively after writing said data to said main memory at said address.
 3. A data processor system including: a. a plurality of processing units, each processing unit including: i. a main memory which stores data and instructions, ii. a processor which processes data by use of instructions, iii. a controller having a controller memory, iv. first signal lines coupling said controller to said main memory, v. second signal lines coupling said controller to said processor; and vi. third signal lines coupling said controller to a controller in at least one other processing unit, each controller adapted to: (1) select one of the memory access from said second signal lines and said third signal lines based on said selected memory access, (2) write data into said main memory based on said selected memory access based on said selected memory access, (3) store said written data into said controller memory. (4) write data into said main memory based on said selected memory access, and (5) send the stored data to at least one controller in another of the plurality of processing units using the third signal lines.
 4. A data processor system according to claim 3 , wherein a memory access includes an address and data, said controller memory includes an address queue and a data queue and said controller stores said data and said address in said data queue and address queue respectively after writing said data to said main memory at said address. 